1. Field of Invention
This invention relates to devices and methods for enabling use of light weight components as part of a robot manipulator system. More specifically, the present invention involves the use of control devices and methods for reducing unwanted elastic vibration or repeated deflection within the robot linkage.
2. Prior Art
The control systems used in current industrial robots are generally based on the assumption that all links which guide the robot manipulators are structurally rigid throughout the course of movement. Specifically, these control systems do not account for the occurrence of elastic deflection or other vibrational movement which could occur if the links making up the robot are or not absolutely rigid. Accordingly, such control systems presume that the only movement within the robot arm is that which is the result of controlled movement actuated by a computer or other form of robot drive system, modified by error correction algorithms and methods which are designed to re-orient the robot manipulator with respect to a particular frame of reference. Included within such movements would be allowances for tolerance within connecting joints and robot drive systems.
In order to force manipulators to conform to the rigid link model which dominates current robot technology, industrial robots are generally built with very stiff links. In order to maintain this stiffness, link components are typically very massive. For example, a survey of industrial robots presently on the market shows an average robot-to-payload weight ratio of about 50. This means that a robot capable of handling a 50 pound load would weight in excess of one ton. By utilizing these stiff and massive links, elastic vibration or deflection within the robot manipulator is maintained at substantially nominal levels.
Although current trends favoring heavy construction of massive robot linkage avoids introduction of elastic deflection and other unwanted movement within the robot structure, such heavy construction extracts a heavy price, not only in cost of robot structures and drive systems, but also large space and support requirements. Therefore, robotic equipment in industrial applications is generally very expensive and requires substantial operating space, further increasing overhead costs. As a consequence, the availability of robotic devices for general use of both large and small manufacturing operations has been limited. Only the largest of industries have generally been able to afford robotic systems to support their manufacturing operations. The extreme weight and high cost of robot devices have precluded expansion of robotics into the small business arena, and particularly within the consumer market.
In addition to conventional applications of robots, the need for robot manipulators in outer space has opened a whole new field of application. Unfortunately, here the extreme weight of conventional robot manipulators poses serious problems to the space industry which must transport such robots into orbit. The large mass and extensive size requirements of current robot manipulators translates into high dollar cost as payload in an orbital spacecraft. Nevertheless, it is common knowledge that robotic devices fulfill a unique role in exploring and conquering the challenges of extra-terrestrial travel and development.
The development of a manipulator control system capable of accurately controlling a robot with lightweight flexible links has been recognized as an important step in the technical development of low cost robots that can be applied in small industry and by the private consumer. Unfortunately, lightweight robots are generally characterized by flexible links. Such flexible links experience large elastic vibrations which are induced by inertial forces affecting the robot links during movement. Such vibrations make it very difficult to perform tasks quickly. The current solution to this problem has been to move the robot linkage very slowly, or to wait for long periods of time between movements to allow the induced vibrations to dampen out. Some efforts to enhance this dampening process have been applied to robot linkage, such as wrapping the linkage with a sheath or other flexible material to absorb the vibrational movement developed within the robot arm or manipulator. None of these techniques has been acceptable. The high robot-to-payload weight ratio remains a major hurdle in advancing the robotics industry to its next stage of economic development and commercial acceptance for wide scale application.